English rare word list mainly cited from below.
- https://phrontistery.info/a.html
- https://grammar.yourdictionary.com/50-rare-words-that-are-useful-to-know.html
- https://www.lexico.com/explore/weird-and-wonderful-words
- http://tolkiengateway.net/wiki/Uncommon_words
- https://7esl.com/english-idioms/
- https://www.idioms4you.com/frequency/Idiom_Usage_Frequency_Index.html
- https://en.wikipedia.org/wiki/English-language_idioms
- https://www.fluentu.com/blog/english/english-idioms-6/
- https://www.bkacontent.com/40-popular-idioms-and-their-meanings/
- https://www.thoughtco.com/common-english-idioms-3211646
- https://lemongrad.com/idioms-with-meanings-and-examples
細かすぎるから一旦パス。